Well-lubricated bicycle wheel problem

[tatertot560]

Homework Statement

A well-lubricated bicycle wheel spins a long time before stopping. Suppose a wheel initially rotating at 170 rpm takes 70 s to stop.

A)If the angular acceleration is constant, how many revolutions does the wheel make while stopping?

Homework Equations

i used circular motion kinematics equations.

The Attempt at a Solution

i changed 170 rpm to 17.80 rad/s. then i used wf=wi+(alpha)(delta)t
wf=17.80 rad/s + (0-70s) = -52.2 rad/s^2
i used (theta)F= (theta)i + wi (delta)t +1/2 ((alpha)(delta)t)^2

i think i used the right equations but when i solve for wf i get -581 rad... don't know if that's the right answer.

i'd greatly appreciate the help :)

 

[Carid]

I think you are making this unnecessarily complex.

If the wheel starts at 170rpm at T=0 and is at 0rpm at T=70 and we know the deceleration is constant, what rotational speed was it turning at at T=35?
If we know that what can we do with that information?

Beware of rpm and revs per second!